When a validated linear standard curve for one analyte is already known, enter its slope and intercept plus a measured sample signal. The calculator solves the line for concentration and reverses a separately entered dilution factor.

Formula: measured aliquot mg/mL = (sample signal − intercept) ÷ slope; original sample mg/mL = measured aliquot mg/mL × dilution factor

Worked example

If signal is 0.52, slope is 0.10 signal per mg/mL and intercept is 0.02, the measured aliquot is 5 mg/mL. With a documented fivefold dilution, the original sample is 25 mg/mL.

A curve must already exist for this analyte

This page does not fit standards or determine whether a calibration is linear. Use a curve with a validated response range and the same signal and concentration units. NIST calibration material describes solving a straight-line signal relationship for concentration.

Dilution factor is explicit

Enter 1 for an undiluted measurement. A fivefold dilution means the measured aliquot concentration is one fifth of the original under a conserved-analyte assumption. Verify any actual preparation and recovery losses outside this tool.

Interpretation limits

A signal below the entered intercept is rejected rather than reported as a negative concentration. An in-range result still does not establish chemical identity, assay quality, precision, clinical suitability or a dose. Arithmetic stays in the browser.

Explore the related calculation

For a different starting point, try the mixed solution concentration calculator or return to the main calculator. Browse the complete tool directory for this site.

Reference and corrections

The definitions and assumptions above follow these sources; the examples and calculator arithmetic are original to this page.

nvlpubs.nist.gov reference

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Standard curve concentration calculator

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